In the process for manufacturing semiconductor elements, liquid-crystal devices or the like, resist film is formed on a substrate, and the resist film is then exposed to light and developed so as to form resist patterns.
Resist patterns have rapidly become finer in recent years as lithographic technology develops further. To form finer patterns, it is an option to shorten irradiation wavelengths. In particular, irradiation wavelengths are shifting from g-line (wavelength: 438 nm) or i-line (wavelength: 365 nm) to deep ultraviolet (DUV) with a wavelength of 300 nm or shorter. Nowadays, lithographic technology using KrF excimer lasers (wavelength: 248 nm) or ArF excimer lasers (wavelength: 193 nm) is employed.
Also, EUV (wavelength: 13.5 nm) lithography with even shorter wavelengths is now being researched. In addition, electron-beam lithographic technology and immersion technology to conduct exposure treatment in liquid such as water or the like are being studied intensively.
In a lithographic process, other than resist film, various thin films such as antireflection film, gap-fill film, top coat film and the like are also used. To form such films, material containing a polymer is usually used.
In the process for manufacturing high-density ICs, computer chips, computer hard drives or the like, metal contamination often causes an increase in defects and a reduction in manufacturing yield, resulting in lower performance of such products.
For example, if impurities of metals such as sodium or iron (metal ions, metal powders, transition metal complexes and the like) are present in a polymer used in a lithographic process, metal contamination may occur during a removal process by plasma.
As fine-process technologies such as lithographic technologies advance, electronic devices are becoming more precise, making the aforementioned problems harder to solve completely. Metal impurities at a very low concentration level are often observed to cause a decrease in performance and stability of semiconductor devices. Especially, light metals such as sodium and heavy metals such as iron are known as main causes of those problems when they are contained in a polymer to be used in a lithographic process. Moreover, metal impurities contained in a polymer at a concentration lower than 100 ppb are identified to cause an adverse impact on performance and stability of electronic devices.
Conventionally, metal impurity concentrations in a polymer have been controlled by selecting material that has passed strict regulations governing impurity concentrations or by conducting thorough process management so that metal impurities will not be mixed into a polymer during its production process. However, as regulations for metal impurity concentrations are becoming even stricter, it is necessary to produce a polymer by a method capable of performing essential controls on metal contamination.
A method is proposed for reducing metal impurities in a polymer by passing a polymer solution through a filter that does not contain a strongly acidic ion-exchange group but contains a charge control agent for generating zeta potential (patent publication 1).
Also, another method proposed is conducted by combining the following steps: in step (T1), a polymer solution is set to come in contact with a cation-exchange resin; in step (T2), the polymer solution is set to come in contact with a mixed resin of a cation-exchange resin and an anion-exchange resin; and in step (T3), the polymer solution is set to pass through a filter that contains material charged with positive zeta potential (patent publication 2).